This invention relates to a developer density detecting apparatus for use with a copying machine.
A prior art device for detecting developer density includes a slanted plate mounted adjacent to a developing roll such as a magnetic brush roll for receiving scraped off developers from the developing roll and carrying them downwardly towards a detector roll assembly which comprises a sleeve and a semi-circular magnet attached to the inner periphery of the sleeve. The developers are attracted onto the sleeve by the action of the magnet and contact with a conductive glass as the sleeve rotates to thereby transfer toners onto the conductive glass. The conductive glass has mounted thereon a light emitting device and a light receiving device which in cooperation photoelectrically detect toner density adhered to the conductive glass. Since developer density is proportional to toner density, developer density can be detected by detecting toner density.
This kind of developer density detecting apparatus is disadvantageous in that developers scraped off by a pile height regulating plate tend to adhere to an outer peripheral portion of the sleeve where no magnet exists by the magnetic force of both ends of the simi-circular magnet when regulating pile height with the developers adhered to the sleeve to a constant height with the pile height regulating plate. Further, magnetic flux density decreases as the thickness of the sleeve increases. Therefore, amount of developers adhered to the sleeve decreases where opposite polarities face each other. As a result, thickness of the adhered developers becomes irregular resulting in an uneven application of toners onto the conductive glass.